It is well established that tumours, even those of the same type, have different genetics and forms.

This variation not only exists between tumours from different patients but also across parts of the very same tumour.

It remains largely unknown to what extent the proteins in any given tumour varies.

In a study described in MCP, Martin Beck and a group of researchers at the European Molecular Biology Laboratory attempt to find out.

"We were interested to find out if the proteins contained within individual cells of the tumour are the same or different," Beck said.

The researchers used laser-capture microdissection to profile protein expression in different parts of sample biopsies from patients with hepatocellular carcinoma, the most common type of liver cancer.

They first quantified differences of protein expression between the tumour tissue and the normal tissue immediately adjacent to it, finding some well-known HCC markers and a few novel candidate biomarkers.

Then the researchers dissected regions within the tumour mass.

They found significant variations in expression of multiple proteins between areas from the center and the periphery of the tumour.

"We could show that, even between seemingly identical cells with the same morphology and the same genome, there are surprisingly pronounced differences on the level of the proteins," Beck said.

He continued "Even proteins that have been proposed as such biomarkers are not evenly distributed across the tumour"

This finding is of immediate clinical importance.

Only a small fraction of a tumour can be obtained in a diagnostic or pretreatment biopsy, and thus the region of withdrawal could have a direct impact on the acquired expression profile.

"It is possible that the tissue sample taken during biopsy does not reflect the actual state of the entire tumor," Beck said.

Beck said the method developed in this study not only allows for studying heterogeneity within a particular tumor but also can improve cancer proteomics research in general.

For example, he said, it may be useful for designing future biomarker discovery studies.

Source: American Society for Biochemistry and Molecular Biology